1. Field of the Invention
The present invention relates to a beam tracking method at the time of terminal blocking in a millimeter wave communication system and a terminal including the same.
2. Description of Related Art
In the 5G mobile communication system, since a transmission speed of 1,000 times or more is required compared to the present LTE, studies on a communication system using a millimeter wave (mmWave) band have been actively conducted. The millimeter wave band has a wide frequency band, strong signal straightness, and forms sharp beams with small antenna arrays, thereby providing high transmission capacity.
The millimeter wave communication system considers an analog beamforming scheme with a single chain rather than a digital beamforming scheme, due to an analog to digital (A/D) converter requiring high sampling frequency and the price burden of an RF chain. That is, the millimeter wave communication system uses codebook based switched beamforming as the analog beamforming scheme. In the switched beamforming, a large gain may be obtained when a beam of a transmitting side and a beam of the receiving side, that is, a pair of beams maximizing an SNR are aligned. Therefore, the millimeter wave communication requires beam training, i.e., a process of finding a pair of optimal transmitting and receiving beams In general, the beam training takes time proportional to the product of the number of the transmitting and receiving antenna beams, and therefore takes a lot of time.
On the other hand, in the millimeter wave communication system, since a beam width is very narrow, a mismatch between the beams may be caused even in a small behavior change of the terminal. The mismatch between the beams causes a sharp attenuation of the received signal. The reception environment change of the terminal may be caused by the beam signal attenuation caused by the reception environment change such as a signal obstruction caused by an external moving object, and a body contact of an antenna, or the mismatch between the beams caused by the behavior changes of the terminal such as a rotation of the terminal and a displacement of the terminal. In this case, in order to find a best beam, the entire process of the beam training is performed again, which leads to a long time consuming problem.